Chapter 2 Cognitive Neuroscience

Some Questions to Consider What is cognitive neuroscience, and why is it necessary? How is information transmitted from one place to another in the nervous system? How are things in the environment, such as faces and trees, represented in the brain? Is it possible to read a person’s mind by measuring the activity of the person’s brain?

Building Blocks of the Nervous System Neurons: cells specialized to receive and transmit information in the nervous system Each neuron has a cell body, an axon, and dendrites

Building Blocks of the Nervous System Cell body: contains mechanisms to keep cell alive Axon: tube filled with fluid that transmits electrical signal to other neurons Dendrites: multiple branches reaching from the cell body, which receives information from other neurons Sensory receptors: specialized to respond to information received from the senses

Caption: A portion of the brain that has been treated with Golgi stains shows the shapes of a few neurons. The arrow points to a neuron’s cell body. The thin lines are dendrites or axons.

How Neurons Communicate Measuring action potentialsaction potentials –Microelectrodes pick up electrical signal –Placed near axon –Active for ~1 second

How Neurons Communicate Measuring action potentials –The size is not measured; size remains consistent –The rate of firing is measured Low intensities: slow firing High intensities: fast firing

How Neurons Communicate Synapse: space between axon of one neuron and dendrite of another When the action potential reaches the end of the axon, synaptic vesicles open and release chemical neurotransmitters Neurotransmitters cross the synapse and bind with the receiving dendrites

How Neurons Communicate Neurotransmitters: chemicals that affect the electrical signal of the receiving neuron –Excitatory: increases chance neuron will fire –Inhibitory: decreases chance neuron will fire

How Neurons Process Information Not all signals received lead to action potential The cell membrane processes the number of impulses received An action potential results only if the threshold level is reached –Interaction of excitation and inhibition

Localization of Function Lobes of the Cerebral Cortex Frontal –Reasoning and planning –Language, thought, memory, motor functioning Parietal –Touch, temperature, pain, and pressure Temporal –Auditory and perceptual processing –Language, hearing, memory, perceiving forms Occipital –Visual processing

Localization of Function: Limbic System Hippocampus: forming memories Amygdala: emotions and emotional memories Thalamus: processing information from vision, hearing, and touch senses

Localization of Function: Perception Primary receiving areas for the senses –Occipital lobe: vision –Parietal lobe: touch, temperature, pain –Temporal lobe: hearing, taste, smell Coordination of information received from all senses –Frontal lobe

Localization of Function: Perception Fusiform face area (FFA) responds specifically to faces –Temporal lobe –Damage to this area causes prosopagnosia (inability to recognize faces) Parahippocampal place area (PPA) responds specifically to places (indoor/outdoor scenes) –Temporal lobe Extrastriate body area (EBA) responds specifically to pictures of bodies and parts of bodies

Localization of Function: Language Language production is impaired by damage to Broca’s area –Frontal lobe Language comprehension is impaired by damage to Wernicke’s area –Temporal lobe Severe Broca’s Aphasia Expressive Aphasia Werneckie’s Aphasia

Caption: Broca’s and Wernicke’s areas were identified in early research as being specialized for language production and comprehension.

Distributed Processing in the Brain In addition to localization of function, specific functions are processed by many different areas of the brain Many different areas may contribute to a function

Putting it all Together: Brain Imaging Positron Emission Tomography (PET) –Blood flow increases in areas of the brain activated by a cognitive task –Radioactive tracer is injected into person’s bloodstream –Measures signal from tracer at each location of the brain –Higher signals indicate higher levels of brain activity

Caption: (a) Person in a brain scanner. (b) In this cross section of the brain, areas of the brain that are activated are indicated by the colors. Increases in activation are indicated by red and yellow, decreases by blue and green

Method: Brain Imaging Functional Magnetic Resonance Imaging (fMRI) –Subtraction technique –Measures blood flow through magnetic properties of blood –Advantage: no radioactive tracer needed

Method: Event-Related Potential (ERP) Neuron “firing” is an electrical event Measure electrical activity on the scalp and make inferences about underlying brain activity Averaged over a large number of trials to calculate ERPs Advantage: continuous and rapid measurements Disadvantage: does not give precise location

Caption: (a) Person wearing electrodes for recording the event- related potential (ERP). (b) An ERP to the phrase “The cats won’t eat.”

Representation in the Brain Feature detectors: neurons that respond best to a specific stimulus Hubel & Wiesel (1965) –Simple cells: neurons that respond best to bars of light of a particular orientation –Complex cells: neurons that respond best to an oriented bar of light with a specific length

Representation in the Brain Specificity coding: representation of a specific stimulus by firing of specifically tuned neurons specialized to just respond to a specific stimulus Distributed coding: representation by a pattern of firing across a number of neurons